Oligohydramnios
Roya Sohaey, MD
DIFFERENTIAL DIAGNOSIS
Common
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Preterm Premature Rupture of Membranes (PPROM)
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Intrauterine Growth Restriction (IUGR)
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Bilateral Renal Anomaly
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Renal Agenesis
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Ureteropelvic Junction Obstruction (UPJ)
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Multicystic Dysplastic Kidney (MCDK)
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Autosomal Recessive Polycystic Kidney Disease
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Bladder Outlet Obstruction
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Posterior Urethral Valves
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Urethral Atresia
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Less Common
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Twin-Twin Transfusion Syndrome
Rare but Important
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Prune Belly Syndrome
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
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Diagnosis of oligohydramnios
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Subjective
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↓ Pockets of fluid
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Fetus:fluid ratio > 1:1
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Objective
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Maximum vertical pocket is ↓ 2 cm
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Amniotic fluid index < 5 cm
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Helpful Clues for Common Diagnoses
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Preterm Premature Rupture of Membranes (PPROM)
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Clinical diagnosis
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Etiology
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Spontaneous
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Infection
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Post-amniocentesis
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Worse prognosis if PPROM early or prolonged
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Early: PPROM < 25 weeks
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Prolonged: PPROM > 14 days
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Intrauterine Growth Restriction (IUGR)
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Estimated fetal weight < 10th percentile
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Oligohydramnios often earliest finding
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Causes
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Placental insufficiency
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Fetal aneuploidy/syndrome
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Doppler assessment
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↑ Umbilical artery resistance
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↑ Uterine artery resistance
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↓ Middle cerebral artery resistance
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Renal Agenesis
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Ultrasound findings
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Anhydramnios (no fluid)
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Absent kidneys and bladder
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No renal arteries (color Doppler)
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Clubfeet, other joint contractures
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Pitfalls
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May have normal fluid early (< 17 weeks)
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Bladder secretions may mimic urine
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Adrenal gland may mimic kidney
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Bowel in renal fossa may mimic kidney
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Fatal prognosis
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Pulmonary hypoplasia
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Ureteropelvic Junction Obstruction (UPJ)
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Ultrasound findings
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↑ Renal pelvis is hallmark finding
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Renal pelvis ≥ 7 mm after 33 weeks
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Associated caliectasis
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No distended ureter or bladder
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Evaluate contralateral kidney
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Bilateral UPJ in 10%
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UPJ + contralateral renal anomaly in 25%
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Prognosis
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Depends on severity of obstruction
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Post-obstructive cystic dysplasia
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Multicystic Dysplastic Kidney (MCDK)
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Renal tissue replaced by cysts
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Ultrasound findings
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Multiple variable-sized cysts
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Kidney may lose reniform shape
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↑ Renal size initially, then ↓
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Severe oligohydramnios if bilateral
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20% of MCDK are bilateral (anhydramnios)
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40% have contralateral renal anomaly
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Poor prognosis if bilateral anomalies
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Autosomal Recessive Polycystic Kidney Disease
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Single gene disorder
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Distal tubule/collecting duct dilatation
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Ultrasound findings
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Enlarging echogenic kidneys
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Majority detected > 24 weeks
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Macrocysts rarely seen
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Variable oligohydramnios
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Perinatal, neonatal, infantile and juvenile presentations
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Perinatal form with 30-50% mortality
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Hepatic fibrosis (rarely in utero)
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Posterior Urethral Valves
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Partial or complete obstruction
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“Keyhole” appearance
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↑ Bladder + ↑ posterior urethra
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Variable hydronephrosis/hydroureter
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± Post-obstructive renal cystic dysplasia
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Spontaneous decompression may occur
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In-utero treatment if severe oligohydramnios
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Serial bladder drainage
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Vesicoamniotic shunt
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In female fetuses, consider urethral atresia
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Helpful Clues for Less Common Diagnoses
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